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Supplementary Figures S1-S5 Supplementary Tables S1-S3 revised

Patients with cancer, in particular patients with hematologic malignancies, are at increased risk for critical illness upon COVID-19. We here assessed antibody as well as CD4+ and CD8+ T-cell responses in unexposed and SARS-CoV-2–infected patients with cancer to characterize SARS-CoV-2 immunity and to identify immunologic parameters contributing to COVID-19 outcome. Unexposed patients with hematologic malignancies presented with reduced prevalence of preexisting SARS-CoV-2 cross-reactive CD4+ T-cell responses and signs of T-cell exhaustion compared with patients with solid tumors and healthy volunteers. Whereas SARS-CoV-2 antibody responses did not differ between patients with COVID-19 and cancer and healthy volunteers, intensity, expandability, and diversity of SARS-CoV-2 T-cell responses were profoundly reduced in patients with cancer, and the latter associated with a severe course of COVID-19. This identifies impaired SARS-CoV-2 T-cell immunity as a potential determinant for dismal outcome of COVID-19 in patients with cancer.Significance:This first comprehensive analysis of SARS-CoV-2 immune responses in patients with cancer reports on the potential implications of impaired SARS-CoV-2 T-cell responses for understanding pathophysiology and predicting severity of COVID-19, which in turn might allow for the development of therapeutic measures and vaccines for this vulnerable patient population.See related commentary by Salomé and Horowitz, p. 1877.This article is highlighted in the In This Issue feature, p. 1861

Purpose Acute B-lymphoblastic leukemia (B-ALL) is a malignant disease characterized by accumulation of clonal immature lymphocytes in the bone marrow and peripheral blood. The approval of BCR::ABL1 tyrosine kinase inhibitors (TKI) such as imatinib, dasatinib, nilotinib and ponatinib marked a milestone in targeted therapy only for a subset of patients carrying the translocation t(9;22)(q34;q11). Immunotherapy with the bispecific antibody (bsAb) blinatumomab targeting CD19xCD3 revolutionized treatment of all B-ALL cases. The combination of both TKI and bsAb, so-called “dual targeting”, is currently under clinical investigation, although TKI might influence T cell effects. Methods We here investigated the combination of different TKI and blinatumomab in BCR::ABL1+ and BCR::ABL1− B-ALL cell lines and primary samples regarding T cell proliferation, differentiation, cytokine release and killing of tumor cells. Results In vitro analysis revealed profound reduction of T cell proliferation, differentiation, cytokine release and killing of tumor cells upon application of BCR::ABL1 TKI with blinatumomab. Inhibition was more pronounced with dasatinib and ponatinib compared to nilotinib and imatinib. T cell signalling after CD3 stimulation was impaired by TKI mirrored by inhibition of LCK phosphorylation. This known off-target effect might influence the efficacy of bsAb therapy when combined with BCR::ABL1 TKI. Conclusion In conclusion, we propose that nilotinib and imatinib might also be suitable substances for combination with blinatumomab and suggest evaluation in clinical trials.

T cell immunity is central for the control of viral infections. CoVac-1 is a peptide-based vaccine candidate, composed of SARS-CoV-2 T cell epitopes derived from various viral proteins1,2, combined with the Toll-like receptor 1/2 agonist XS15 emulsified in Montanide ISA51 VG, aiming to induce profound SARS-CoV-2 T cell immunity to combat COVID-19. Here we conducted a phase I open-label trial, recruiting 36 participants aged 18–80 years, who received a single subcutaneous CoVac-1 vaccination. The primary end point was safety analysed until day 56. Immunogenicity in terms of CoVac-1-induced T cell response was analysed as the main secondary end point until day 28 and in the follow-up until month 3. No serious adverse events and no grade 4 adverse events were observed. Expected local granuloma formation was observed in all study participants, whereas systemic reactogenicity was absent or mild. SARS-CoV-2-specific T cell responses targeting multiple vaccine peptides were induced in all study participants, mediated by multifunctional T helper 1 CD4+ and CD8+ T cells. CoVac-1-induced IFNγ T cell responses persisted in the follow-up analyses and surpassed those detected after SARS-CoV-2 infection as well as after vaccination with approved vaccines. Furthermore, vaccine-induced T cell responses were unaffected by current SARS-CoV-2 variants of concern. Together, CoVac-1 showed a favourable safety profile and induced broad, potent and variant of concern-independent T cell responses, supporting the presently ongoing evaluation in a phase II trial for patients with B cell or antibody deficiency., A phase I open-label trial evaluating the immunogencity, reactogenicity and safety of a peptide-based SARS-CoV-2 vaccine candidate to induce SARS-CoV-2-specific T cell responses.

Both B cells and T cells are involved in an effective immune response to SARS‐CoV‐2, the disease‐causing virus of COVID‐19. While B cells—with the indispensable help of CD4+ T cells—are essential to generate neutralizing antibodies, T cells on their own have been recognized as another major player in effective anti‐SARS‐CoV‐2 immunity. In this report, we provide insights into the characteristics of individual HLA‐A*02:01‐ and HLA‐A*24:02‐restricted SARS‐CoV‐2‐reactive TCRs, isolated from convalescent COVID‐19 patients. We observed that SARS‐CoV‐2‐reactive T‐cell populations were clearly detectable in convalescent samples and that TCRs isolated from these T cell clones were highly functional upon ectopic re‐expression. The SARS‐CoV‐2‐reactive TCRs described in this report mediated potent TCR signaling in reporter assays with low nanomolar EC50 values. We further demonstrate that these SARS‐CoV‐2‐reactive TCRs conferred powerful T‐cell effector function to primary CD8+ T cells as evident by a robust anti‐SARS‐CoV‐2 IFN‐γ response and in vitro cytotoxicity. We also provide an example of a long‐lasting anti‐SARS‐CoV‐2 memory response by reisolation of one of the retrieved TCRs 5 months after initial sampling. Taken together, these findings contribute to a better understanding of anti‐SARS‐CoV‐2 T‐cell immunity and may contribute to paving the way toward immunotherapeutics approaches targeting SARS‐CoV‐2., T cell receptors (TCRs) directed against previously identified SARS‐CoV‐2 target epitopes were isolated from convalescent COVID‐19 patients by single‐cell sequencing. Upon ectopic re‐expression, these SARS‐CoV‐2 TCRs conferred potent effector functions such as cytotoxicity and Interferon‐gamma production.

Dose-finding designs for phase-I trials aim to determine the recommended phase-II dose (RP2D) for further phase-II drug development. If the trial includes patients for whom several lines of standard therapy failed or if the toxicity of the investigated agent does not necessarily increase with dose, optimal dose-finding designs should limit the frequency of treatment with suboptimal doses. We propose a two-stage design strategy with a run-in intra-patient dose escalation part followed by a more traditional dose-finding design. We conduct simulation studies to compare the 3 + 3 design, the Bayesian Optimal Interval Design (BOIN) and the Continual Reassessment Method (CRM) with and without intra-patient dose escalation. The endpoints are accuracy, sample size, safety, and therapeutic efficiency. For scenarios where the correct RP2D is the highest dose, inclusion of an intra-patient dose escalation stage generally increases accuracy and therapeutic efficiency. However, for scenarios where the correct RP2D is below the highest dose, intra-patient dose escalation designs lead to increased risk of overdosing and an overestimation of RP2D. The magnitude of the change in operating characteristics after including an intra-patient stage is largest for the 3 + 3 design, decreases for the BOIN and is smallest for the CRM.

Patients with cancer, in particular patients with hematologic malignancies, are at increased risk for critical illness upon COVID-19. We here assessed antibody as well as CD4+ and CD8+ T-cell responses in unexposed and SARS-CoV-2–infected patients with cancer to characterize SARS-CoV-2 immunity and to identify immunologic parameters contributing to COVID-19 outcome. Unexposed patients with hematologic malignancies presented with reduced prevalence of preexisting SARS-CoV-2 cross-reactive CD4+ T-cell responses and signs of T-cell exhaustion compared with patients with solid tumors and healthy volunteers. Whereas SARS-CoV-2 antibody responses did not differ between patients with COVID-19 and cancer and healthy volunteers, intensity, expandability, and diversity of SARS-CoV-2 T-cell responses were profoundly reduced in patients with cancer, and the latter associated with a severe course of COVID-19. This identifies impaired SARS-CoV-2 T-cell immunity as a potential determinant for dismal outcome of COVID-19 in patients with cancer. Significance: This first comprehensive analysis of SARS-CoV-2 immune responses in patients with cancer reports on the potential implications of impaired SARS-CoV-2 T-cell responses for understanding pathophysiology and predicting severity of COVID-19, which in turn might allow for the development of therapeutic measures and vaccines for this vulnerable patient population. See related commentary by Salomé and Horowitz, p. 1877. This article is highlighted in the In This Issue feature, p. 1861

Invasive breast cancer (IBC) is the most common malignant disease in women worldwide. In recent years, the landscape of treatment options has rapidly evolved. With the success of checkpoint inhibitors in triple negative IBC, immunotherapy has become standard of care highlighting the strength of T cell-based strategies for anti-tumor therapy. Naturally, the targets of T cell-mediated immune responses are represented by short peptides presented on human leukocyte antigen (HLA) molecules. For several years, huge effort has been made to analyze and characterize HLA-presented tumor antigens to further understand anti-tumor immunity and to identify suitable targets for novel immunotherapy approaches. Aside from membrane-bound HLA molecules, soluble HLA-peptide complexes (sHLA) can be found in a variety of body fluids. These molecules are suggested to impact cellular immune responses, but it is still a matter of debate, whether shifts in sHLA levels contribute to disease outcome or are observed as a consequence of disease. Whereas the role of the non-classical sHLA-G in IBC has been studied showing elevated levels in patients compared to a healthy cohort, data on classical sHLA class I molecules is not yet available. Here, we report on sHLA class I serum levels in patients with IBC after neoadjuvant chemotherapy or combined chemotherapy with antibody treatment (n = 52). We observed higher serum levels of sHLA in neoadjuvant-treated IBC patients without histopathological complete response after neoadjuvant therapy (n = 36) compared to healthy volunteers (n = 84). Patients with locally advanced tumors, according to TNM classification, had a tendency towards lower sHLA levels than patients with small size tumors. Furthermore, sHLA levels were decreased in patients with sentinel node or disseminated axillary lymph node metastases compared to non-metastatic patients. Of note, sHLA levels tended to be elevated in patients with Her2-overexpression (based on immunohistochemistry staining and fluorescence in situ hybridization), whereas for histological hormone receptor expression a tendency towards lower sHLA levels in patients with high expression was observed. Furthermore, sHLA levels were reduced in patients with disseminated tumor cells in bone marrow aspiration. No significant difference in sHLA levels were seen in terms of grading of tumor, prevalence of distant metastasis, menopausal status and elevated tumor markers. Interestingly, we observed a tendency to prolonged progression-free survival in patients with high serum concentrations of sHLA, which will be updated with data from additional patients at the AACR meeting. Taken together, these data provides first insights about sHLA class I in patients with IBC after neoadjuvant treatment suggesting an impact of sHLA and T cell-mediated immune surveillance on survival in patients with IBC. Citation Format: Christian M. Tegeler, Jonas Rieth, André Koch, Dominik Dannehl, Léa L. Volmer, Sabine Matovina, Markus Hahn, Tobias Engler, Andreas D. Hartkopf, Sara Y. Brucker, Juliane S. Walz, Jonas S. Heitmann, Annika Nelde. A correlation of soluble HLA serum levels with clinical data and survival in patients with invasive breast cancer after neoadjuvant treatment. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4376.

The humoral immune response to SARS-CoV-2 is a benchmark for immunity and detailed analysis is required to understand the manifestation and progression of COVID-19, monitor seroconversion within the general population, and support vaccine development. The majority of currently available commercial serological assays only quantify the SARS-CoV-2 antibody response against individual antigens, limiting our understanding of the immune response. To overcome this, we have developed a multiplex immunoassay (MultiCoV-Ab) including spike and nucleocapsid proteins of SARS-CoV-2 and the endemic human coronaviruses. Compared to three broadly used commercial in vitro diagnostic tests, our MultiCoV-Ab achieves a higher sensitivity and specificity when analyzing a well-characterized sample set of SARS-CoV-2 infected and uninfected individuals. We find a high response against endemic coronaviruses in our sample set, but no consistent cross-reactive IgG response patterns against SARS-CoV-2. Here we show a robust, high-content-enabled, antigen-saving multiplex assay suited to both monitoring vaccination studies and facilitating epidemiologic screenings for humoral immunity towards pandemic and endemic coronaviruses., Serology is an important way to monitor SARS-CoV-2 infection in the population and support vaccine development. Here the authors develop a multiplex immunoassay including spike and nucleocapsid proteins of SARS-CoV-2 and the endemic human coronaviruses with high specificity and sensitivity.

T-cell recognition of HLA-presented antigens is central for the immunological surveillance of malignant disease and key for the development of novel T-cell-based immunotherapy approaches. In recent years, large-scale immunopeptidome studies identified naturally presented tumor-associated antigens for several malignancies. Regarding ovarian carcinoma (OvCa), Mucin-16 (MUC16) and Mesothelin (MSLN) were recently described as the top HLA class I- and HLA class II-presented tumor antigens, respectively. Here, we investigate the role and impact of immunopeptidome-presented tumor antigens on the clinical outcomes of 39 OvCa patients with a follow-up time of up to 50 months after surgery. Patients with a HLA-restricted presentation of high numbers of different MSLN-derived peptides on their tumors exhibited significantly prolonged progression-free (PFS) and overall survival (OS), whereas the presentation of MUC16-derived HLA class I-restricted peptides had no impact. Furthermore, a high HLA-DRB gene expression was associated with increased PFS and OS. In line, in silico prediction revealed that MSLN-derived HLA class II-presented peptides are predominantly presented on HLA-DR allotypes. In conclusion, the correlation of MSLN tumor antigen presentation and HLA-DRB gene expression with prolonged survival indicates a central role of CD4

Risk assessment in acute myeloid leukemia (AML) mainly relies on (cyto-)genetic and morphologic features. Nonetheless, further markers are needed to allow for accurate risk stratification. Type I Fc gamma receptors (FcγRs) such as CD16, CD32, and CD64 play an important role in mediating immunomodulatory functions in different myeloid cell types as well as NK and B cells. We here evaluated expression of the three FcγR on peripheral blood AML blasts. Using flow cytometry, we found heterogeneous expression of the FcγR throughout the patient cohort. Correlation of expression levels with disease outcome revealed significantly shorter OS in patients with CD16+ blasts at first diagnosis. CD32 and CD64 expression showed no association with survival but correlated with a mature phenotype and FAB M6. Our data provide clear evidence for the value of immunophenotyping FcγR expression on leukemic cells using peripheral blood, which is rapidly available and improves risk stratification in AML.

Several genetic and molecular markers are general predictors of outcome in acute myeloid leukemia (AML), but only few are predictive of outcomes after allogeneic hematopoietic stem cell transplantation (HSCT). Novel markers are needed to improve treatment decisions regarding HSCT. CD105 (endoglin) is a type I transmembrane protein capable of activating endothelial cells. Moreover, CD105 mediates stem cell properties of hematopoietic stem cells and enables repopulation within the bone marrow. Expression of CD105 on vessels of solid tumors and on AML blasts is correlated with poor prognosis. We recently demonstrated that CD105 expression is an independent predictor of overall survival in AML. However, its role in patients receiving intensive treatment with consecutive allogenic transplantation has not been assessed. Using flow cytometry, we analyzed primary samples of 41 patients who underwent HSCT. Using the previously defined SFI cut-off of 5.2, we identified differences in CD105 expression regarding FAB classification and NCCN risk score. Moreover, we detected differences regarding transplant indication and WHO classification with regards to CD105 surface levels. In patients undergoing HSCT high CD105 expression correlated significantly with poor overall survival. We identify CD105 expression in AML as prognostic marker for outcome after HSCT in AML.

While several genetic and morphological markers are established and serve to guide therapy of acute myeloid leukaemia (AML), there is still profound need to identify additional markers to better stratify patients. CD105 (Endoglin) is a type I transmembrane protein reported to induce activation and proliferation of endothelial cells. In addition, CD105 is expressed in haematological malignancies and the vessels of solid tumours. Here, CD105 associates with unfavourable disease course, but so far no data are available on the prognostic relevance of CD105 in haematological malignancies. We here generated a novel CD105 antibody for analysis of expression and prognostic relevance of CD105 in a cohort of 62 AML patients. Flow cytometric analysis revealed substantial expression in the various AML FAB types, with FAB M3 type displaying significantly lower surface levels. Next we established a cut-off specific fluorescence level of 5.22 using receiver-operating characteristics, which allowed to group patients in cases with CD105lo and CD105hi surface expression and revealed that high CD105 expression correlated significantly with poor overall and progression free survival. In conclusion, we here identify CD105 expression as a novel prognostic marker in AML, which may serve to optimize follow up and treatment decisions for AML patients.

T cell-based immunotherapy, for example, with T cell-recruiting bispecific antibody (bsAb), has revolutionized oncological treatment. However, many patients do not respond to treatment, and long-term remissions are still rare. Several tumor immune evasion mechanisms have been reported to counteract efficiency of T cell-engaging therapeutics. Platelets largely affect cancer pathophysiology by mediating tumor invasion, metastasis, and immune evasion. On treatment of patients in a clinical trial with a PSMA×CD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. On modeling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4+ and CD8+ T-cell reactivity as revealed by impaired T-cell degranulation, secretion of perforin, and ultimately, inhibition of target cell lysis. This effect occurred in a transforming growth factor beta (TGF-β)-dependent manner and was not restricted to PSMA×CD3 bsAb, but rather observed with various CD3-directed bispecific constructs, including the approved CD19×CD3 bsAb blinatumomab. BsAb-mediated T-cell reactivity could be restored by platelet inhibition and specifically by blocking the TGF-β axis. Together, our findings demonstrate that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function as a means to reinforce the effectiveness of bsAb treatment.

Immune-checkpoint inhibitors (ICI) have transformed oncological therapy. Up to 20% of all non-small cell lung cancers (NSCLCs) show durable responses upon treatment with ICI, however, robust markers to predict therapy response are missing. Here we show that blood platelets interact with lung cancer cells and that PD-L1 protein is transferred from tumor cells to platelets in a fibronectin 1, integrin α5β1 and GPIbα-dependent manner. Platelets from NSCLC patients are found to express PD-L1 and platelet PD-L1 possess the ability to inhibit CD4 and CD8 T-cells. An algorithm is developed to calculate the activation independent adjusted PD-L1 payload of platelets (pPD-L1Adj.), which is found to be superior in predicting the response towards ICI as compared to standard histological PD-L1 quantification on tumor biopsies. Our data suggest that platelet PD-L1 reflects the collective tumor PD-L1 expression, plays important roles in tumor immune evasion and overcomes limitations of histological quantification of often heterogeneous intratumoral PD-L1 expression., The definition of biomarkers to predict therapy responses to immune-checkpoint inhibitors represent an unmet clinical need. Here the authors provide evidences that platelet-derived PD-L1 could serve as a prognostic and predictive biomarker in patients with non-small cell lung cancer.

T-cell immunity is central for the control of viral infections. CoVac-1 is a peptide-based vaccine candidate, composed of SARS-CoV-2 T-cell epitopes derived from various viral proteins, combined with the toll-like receptor 1/2 agonist XS15 emulsified in MontanideTM ISA51 VG, aiming to induce superior SARS-CoV-2 T-cell immunity to combat COVID-19. We conducted a Phase I open-label trial, including 36 participants aged 18 to 80 years, who received one single subcutaneous CoVAC-1 vaccination. The primary endpoint was safety analyzed until day 56. Immunogenicity in terms of CoVac-1-induced T-cell response was analyzed as main secondary endpoint until day 28. No serious adverse events and no grade 4 adverse events were observed. Expected local granuloma formation was observed in all study subjects, while systemic reactogenicity was absent or mild. SARS-CoV-2-specific T-cell responses targeting multiple vaccine peptides were induced in all study participants, mediated by multifunctional T-helper 1 CD4+ and CD8+ T cells. CoVac-1-induced interferon-γ T-cell responses by far surpassed those detected in COVID-19 convalescents and were unaffected by current SARS-CoV-2 variants of concern (VOC). Together, CoVac-1 showed a favorable safety profile and induced broad, potent, and VOC-independent T-cell responses, supporting the presently ongoing evaluation in a Phase II trial for patients with B-cell/antibody deficiency. Funded by the Ministry of Science, Research and the Arts Baden-Württemberg, Germany; ClinicalTrials.gov number, NCT04546841.

While highly efficient in hematological malignancies, bispecific antibodies (bsAbs), alike the closely related CAR T cells, are as of yet not successful in solid tumors. Moreover, all presently available T cell-mobilizing strategies cause substantial side effects that endanger patients and limit applicable doses and thus efficacy. Here we report on the development of CC-1, a PSMAxCD3 bsAb that is constructed in a novel IgG-based format (IgGsc) and contains a proprietary PSMA binder with extended reactivity. CC-1 displays a prolonged serum half-life, especially when compared to the BiTE bsAb format. Extensive in vitro and in vivo characterization demonstrated the potency of CC-1 to induce T cell activity in a highly target cell-restricted manner, resulting in profound antitumor activity, which among others allowed for elimination of large established tumors in humanized mice (Zekri et al, EMBO 2020). Exclusively funded by public resources, we conducted GMP production of CC-1 and in November 2019 initiated a first in human trial enrolling castration resistant prostate carcinoma patients (NCT04104607). The trial consists of two parts: a dose escalation phase with intra-individual dose escalation until the target dose of 826µg to determine overall safety, tolerability as well as the maximum tolerated dose (MTD), and a dose expansion phase, where patients are treated on the MTD level to detect possible efficacy. In August 2021, recruitment in the dose escalation phase was completed and the target dose was reached without DLT upon treatment of the 9th patient. A total of 14 patients were treated, with the most frequently observed toxicity being cytokine release syndrome (CRS) in 79% of patients. CRS did not exceed grade 2 according to the Lee et al. grading system (Lee et al., 2014) and resolved in most cases without additional application of tocilizumab. Besides hypertension (observed in 50% of patients), no further CC-1 related toxicities (i.e., Xerostomia, or anaphylactic reaction) were observed. As expected, after prophylactic tocilizumab application decreased neutrophile counts and elevated liver enzymes were observed in 86% and 43% of patients, respectively. In terms of efficacy, a rapid and profound decline of elevated PSA levels was observed in all the heavily pre-treated patients, with up to 60% reduction compared to baseline. Three patients of the dose escalation phase received multiple treatment cycles at the highest dose level, based on clinical tolerability, documented induction of potent T cell activation as well as rapid and profound decline of elevated PSA levels. Taken together, CC-1 is a promising compound with a favorable toxicity profile and promising clinical activity. Recruitment in the dose expansion phase is ongoing with the respective data to be presented at the meeting. Citation Format: Jonas S. Heitmann, Juliane S. Walz, Martin Pflügler, Maddalena Marconato, Christian M. Tegeler, Julia Reusch, Jannik Labrenz, Richard Schlenk, Gundram Jung, Helmut Salih. CC-1, a bispecific PSMAxCD3 antibody for treatment of prostate carcinoma: Results of the ongoing phase I dose escalation trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT141.

Individuals with impaired ability to mount a humoral immune response, either during natural infection or upon prophylactic vaccination, are at high risk for a severe course of COVID-19. Besides humoral immunity mediated by B cells, T cell immunity is key for the control of viral infections. We developed the peptide-based vaccine candidate CoVac-1, which primarily aims for the induction of SARS-CoV-2-specific T cells. CoVac-1 comprises six promiscuous HLA-DR-binding SARS-CoV-2-derived T cell epitopes from various viral proteins proven (i) to be frequently and HLA-independently recognized by T cells in COVID-19 convalescents, (ii) to be of pathophysiological relevance for T cell immunity to combat COVID-19, and (iii) to mediate long-term immunity after infection (Nelde et al. Nat Immunol 2021, Bilich et al. Sci Transl Med 2021). CoVac-1 vaccine peptides are adjuvanted with the novel toll-like receptor 1/2 agonist XS15 emulsified in Montanide࣪ ISA51 VG. In a first-in-human clinical trial in healthy adults (NCT04546841), CoVac-1 showed a favorable safety profile and induced profound and long-lasting T cell immunity after single dose administration in 100% of the study subjects, mediated by multifunctional T-helper 1 CD4+ and CD8+ T cells. CoVac-1-induced T cell responses surpassed those after SARS-CoV-2 infection as well as those after vaccination with approved vaccines and were unaffected by current SARS-CoV-2 variants of concern (Heitmann et al. Nature 2021). Here we present the interim safety and immunogenicity results of our Phase I/II trial evaluating CoVac-1 in patients with congenital or acquired B cell deficiency, mainly comprising leukemia and lymphoma patients (NCT04954469). 64% of study subjects had previously been vaccinated with approved vaccines without developing any humoral immune response. Alike in the healthy adults, CoVac-1 showed a good safety and tolerability profile without relevant systemic adverse events. CoVac-1-specific T cell responses could be documented in 93% of study subjects on day 28 after CoVac-1 application, with earliest responses evidenced at day 14 (71%). Vaccine-induced T cell responses were mediated by multifunctional T-helper 1 CD4+ T cells. Of note, CoVac-1 induced T cell responses in this highly immune compromised study population were similar to those occurring in healthy volunteers after natural infection or induced by approved vaccines. These results identify CoVac-1 as promising vaccine candidate for cancer and other immunocompromised patients with immunoglobulin deficiency. Recruitment of the Phase II part of the trial is ongoing with results expected for March 2022. Citation Format: Claudia Tandler, Jonas S. Heitmann, Maddalena Marconato, Yacine Maringer, Monika Denk, Marion Richter, Annika Nelde, Imma Fischer, Markus W. Löffler, Hans-Georg Rammensee, Helmut R. Salih, Juliane S. Walz. Interim safety and immunogenicity results of a phase I trial evaluating the multi-peptide COVID-19 vaccine candidate CoVac-1 for induction of SARS-CoV-2 T cell immunity in cancer patients with disease- or treatment-related immunoglobulin deficiency [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT258.

Genetic loss of the transcription factor NFAT2 (NFATc1), known as important player in lymphocyte development, causes an aggressive course of CLL, as it enhances BCR signaling and leads to highly malignant and proliferative disease (Märklin et al. Nat Commun 2017). To investigate whether and how NFAT2 affects treatment resistance in CLL, we generated a CRISPR/Cas9 based NFAT2 knockout (KO) in MEC-1 CLL cells to model aggressive CLL. In immunodeficient NSG-mice, the NFAT2 KO cells showed a ten-fold higher engraftment in the bone marrow after three weeks compared to scrambled (SCR) controls. Cytotoxicity assays revealed a profoundly higher resistance of NFAT2 KO cells to NK cell killing without detectable differences at the level of recognition as revealed by analyses of NK cell activation, degranulation and IFNy release, which excluded resistance to NK cells was due to altered immunogenicity. As CLL patients are routinely treated with anti-CD20 antibody Rituximab, which mediates its therapeutic efficacy in large part by inducing antibody dependent cellular cytotoxicity (ADCC) of NK cells via secretion of perforin and granzymes. When we exposed the target cells to the cytotoxic content isolated out of NK cells, MEC-1 NFAT2 KO cells showed higher resistance for membrane permeabilization compared to SCR controls. In line, perforin blockade equalized susceptibility to membrane permeabilization of both, NFAT2 KO cells and controls, confirming the involvement of NFAT2 in maintaining membrane integrity. In addition, caspase 3/7 activation was reduced in NFAT2 KO cells upon exposure to NK cell granule content as well as upon treatment with staurosporine. This shows an important role of NFAT2 for resistance of the leukemic cells at early stages of apoptosis. The results on the role of NFAT2 in resistance to NK effector function were confirmed with primary CLL patient cells, which were grouped according to high and low NFAT2 expression followed by treatment with NK cell content. Our results demonstrate that loss of NFAT2 allows CLLs cells to evade NK cell effector function. This holds true for both, constitutive cytotoxicity and therapeutically induced ADCC and is due to lowered susceptibility of the leukemic cells to perforin mediated membrane permeabilization and intrinsic resistance to granzyme induced apoptosis. Thus, NFAT2 loss, which correlates with aggressive clinical course in patients, facilitates resistance of CLL cells to CD20 antibody-based treatment. Citation Format: Samuel J. Holzmayer, Sarah M. Greiner, Kuebra Kaban, Jonas S. Heitmann, Helmut R. Salih, Melanie Maerklin. NFAT2 determines susceptibility of chronic lymphocytic leukemia cells to constitutive and Rituximab-induced NK cell killing [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2102.

Prostate cancer is the second most common malignancy in men with radical prostatectomy and radio-therapy being the primary curative treatment modalities in localized disease. However, up to 30% of patients experience recurrence that frequently leads to the development of metastatic disease associated with poor outcome. Therefore, novel, effective and low-side effect treatment options are essential, in particular for elderly and frail prostate cancer patients not eligible for intense therapy. Whereas, immune checkpoint inhibitors showed limited efficacy in prostate cancer so far, targeted T cell-based approaches with bispecific antibodies and cancer vaccines achieved promising results in this tumor entity. In this study, we established a prostate-associated off-the-shelf peptide warehouse, using mass-spectrometry-based immunopeptidome analysis of a large cohort of primary prostate tissue (n = 51), for the development of a broadly applicable personalized vaccine. The prostate dataset (23 prostate cancer, 12 adjacent benign, 16 benign prostate samples) comprising 29,893 HLA class I and II molecules, was compared to the immunopeptidomes of various benign non-prostate tissues (HLA-Ligand Atlas) to identify prostate exclusive antigens. Further antigen selection was based on the high presentation frequency. In total, 30 frequently expressed and prostate exclusive HLA class I peptides restricted to the six common allotypes HLA-A*02, -A*03, -A*24, -B*07, -B*08 and -B*40, covering more than 76% of the world population for at least one allotype, and five promiscuous HLA-DR restricted peptides found in up to 37% of prostates were selected. Immunogenicity was validated by IFNγ ELISPOT screening for preexisting T cell responses, as well as by in vitro priming experiments of naïve T cells in prostate cancer patients and healthy volunteers. The peptide warehouse will enable the formulation of personalized vaccines based on individual HLA allotype and immunopeptidome analysis of patient’s tumor samples in a reasonable time and cost frame within large cohort studies. We provided first evidence for the feasibility of this approach by designing a personalized immunopeptidome-guided peptide vaccine for a patient with metastatic prostate cancer. The vaccine was adjuvanted with the toll-like receptor 1/2 agonist XS15 emulsified in Montanide࣪ ISA51 VG and applied three times within a 12-week interval. Induction of a profound T cell response targeting 7/9 (78%) vaccine peptides was observed one week after the second vaccination. T cell responses have been persisting for almost two years in the patient, and in combination with androgen deprivation therapy enabled persistent PSA remission. In conclusion, we designed an immunopeptidomics-guided peptide warehouse and provided first evidence for its personalized application in prostate cancer patients. Citation Format: Yacine Maringer, Lena Freudenmann, Annika Nelde, Jonas S. Heitmann, Helmut R. Salih, Marissa Dubbelaar, Jörg Hennenlotter, Arnulf Stenzl, Jens Bedke, Hans-Georg Rammensee, Juliane S. Walz. Immunopeptidomics-guided tumor antigen warehouse design and first clinical application of a personalized peptide vaccine for prostate cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3556.

Immunotherapeutic strategies such as T cell-recruiting bispecific antibodies (bsAb), chimeric antigen receptor (CAR) T cells, and immune checkpoint inhibition have revolutionized oncological treatment. However, many patients do not respond to treatment with the so far available therapeutics, others for limited time only. Various tumor immune evasion mechanisms have been reported to counteract efficiency of T cell engaging therapeutics. Thrombocytes have recently been described to affect cancer biology by mediating epithelial-mesenchymal transition, tumor invasion, metastasis and notably also immune evasion. Here we report that, upon treatment of prostate cancer patients within a clinical trial evaluating a novel PSMAxCD3 bsAb (NCT04104607), we observed profound treatment-associated platelet activation, mirrored by a decrease of total platelet count. Upon modelling the treatment setting, we found that platelet activation significantly reduced bsAb-mediated CD4+ and CD8+ T cell reactivity as revealed by impaired T cell activation, reduced secretion of perforin and ultimately inhibition of target cell lysis. The immunosuppressive effect mediated by platelets occurred in a TGFβ-dependent manner and was not restricted to the PSMAxCD3 bsAb, but was also observed with various other CD3-directed bispecific constructs including the clinically approved CD19xCD13 bsAb Blinatumomab. BsAb-mediated T cell reactivity could generally be restored by inhibiting platelets using dabigatran, but also specifically by blocking the TGFβ axis. Together, our findings unravel that platelets undermine the efficacy of T cell-recruiting bsAb and identify modulation of platelet function and TGFβ as means to reinforce the effectiveness of bsAb treatment. Citation Format: Martina S. Lutz, Boris Klimovich, Stefanie Maurer, Jonas S. Heitmann, Melanie Maerklin, Latifa Zekri, Gundram Jung, Helmut R. Salih, Clemens Hinterleitner. Platelet-derived TGFβ undermines treatment efficacy of t cell recruiting bispecific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2859.

Acute myeloid leukemia (AML) is the most common form of acute leukemia in adults. Untreated, AML leads to death within months after first symptoms. Combinatorial chemotherapy, mostly using a pyrimidine analog together with an anthracycline, made this previously incurable disease medicable, and response to remission-inducing chemotherapy strongly correlates with patient outcome. Despite advances in treatment over the recent years, AML still has a poor prognosis with an average 5-year survival rate of 30%. A better understanding of the molecular mechanisms predicting and affecting treatment efficacy is key to improve disease control and outcome. Here we studied the expression, prognostic relevance and functional role of the tumor necrosis factor receptor (TNFR) family member Receptor Activator of Nuclear Factor (NF)-κB (RANK) in AML. We conducted an experimental ex vivo study using leukemic cells of 54 AML patients. Substantial surface expression of RANK was detected on the primary AML cells in 35% of the analyzed patients. We further found that RANK signaling induced the release of the cytokines IL-6, IL-8, TNF and IL-10 acting as growth and survival factors for the leukemic cells and mediated resistance of AML cells to treatment with doxorubicin and cytarabine, the most commonly used cytostatic compounds in AML treatment. In line, prevalence of RANK expression on leukemic cells correlated with dismal disease course of patients as revealed by reduced overall survival. Together, our results show that RANK plays a yet unrecognized role in AML pathophysiology and resistance to treatment. Moreover, the association of RANK expression with adverse disease course identifies RANK as potential “functional” prognostic marker and putative target for therapeutic intervention to improve treatment response of AML patients. Citation Format: Kim L. Clar, Lisa M. Weber, Bastian J. Schmied, Jonas S. Heitmann, Maddalena Marconato, Claudia Tandler, Pascal Schneider, Helmut R. Salih. Receptor Activator of NF-κB (RANK) confers resistance to chemotherapy in AML and associates with dismal disease course [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3957.

After diagnosis, a primary goal of treatment in acute myeloid leukemia (AML) is to achieve a morphological complete remission (CR) by induction chemotherapy. However, about half of the patients in CR show remaining minimal residual disease (MRD), which constitutes the basis for relapse. With the aim to eradicate MRD and thus improve long-term survival in AML, we recently conducted a phase I trial evaluating safety/tolerability and preliminary efficacy of an Fc-optimized antibody targeting CD135/FLT3 (FLYSYN, NCT02789254) to induce NK cell anti-leukemia reactivity. This trial enrolling AML patients in CR with detectable MRD revealed that FLYSYN is safe and well tolerated, with about 45% of patients achieving a molecular response after treatment with the target dose (Heitmann et al., Blood 2020). Besides by reinforcing the ADCC-inducing capability of antibodies, NK cell immunity can be further increased by cytokines like IL-15, and multiple efforts presently aim to exploit the latter cytokine for cancer treatment. However, clinical efficacy of IL-15 so far is limited as systemic application causes substantial side effects due to unspecific immune activation (Conlon et al, JCO 2015). To overcome this limitation, we aimed to develop an immunocytokine consisting of our Fc-optimized CD135 mAb fused to IL-15. However, the activity of the cytokine moiety within classical ICs does not depend on antigen binding, and thus application of clinically effective doses is still prevented by toxicity due to unspecific immune activation. To overcome this problem, we took advantage of the unique mechanism of action of IL-15, which stimulates IL-15Rβ/γ on cytotoxic lymphocytes as membrane-bound complex with IL-15Rα on monocytes and DCs (trans-presentation) and generated an IL-15 mutant with abolished IL-15Rα binding. The latter allows to substitute physiological trans-presentation by binding of the construct to the target antigen, thereby limiting side effects. Functional analysis using primary AML cells as targets revealed that our modified immunocytokine (MIC135) induced target-restricted NK cell anti-leukemia reactivity in a profoundly greater extent than the Fc-optimized FLYSYN antibody. Notably, in stark contrast to FLYSYN, MIC135 induced prominent NK cell proliferation, and target cell killing upon treatment with MIC135 was likewise clearly superior. Analyses regarding off-target toxicity confirmed the target-antigen restricted efficacy of MIC135 compared to anti-CD135 immunocytokine with wildtype IL-15 (IC135). Furthermore, our MIC135 did not induce unwanted effects against healthy FLT3 expressing cells. Taken together, MIC135 induces NK cell reactivity against leukemia cells in a highly target cell-restricted manner and displays higher efficacy than Fc-optimized antibodies, thus constituting a promising treatment option for AML. Citation Format: Martina S. Lutz, Bastian J. Schmied, Fabian Riegg, Latifa Zekri, Jonas S. Heitmann, Melanie Maerklin, Martin Pfluegler, Gundram Jung, Helmut R. Salih. A CD135 immunocytokine with target cell-restricted IL-15 activity for treatment of AML [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2860.